1. Field of the Invention
The present invention relates to a scroll type fluid machine having both a compression mode (pump mode) in which fluid is compressed and discharged, and a expansion mode (motor mode) in which fluid pressure at the time of expansion is converted into kinetic energy and outputted as mechanical energy. The present invention is effectively applied to a compressor with which an expander is integrated into one body, which is used for a vapor-compression type refrigerating machine, having a heat recovery system such as the Rankine cycle by which heat energy is recovered.
2. Description of the Related Art
For example, as shown in the official gazette of Japanese Patent No. 2540738, in the case of a conventional vapor-compression type refrigerating machine provided with the Rankine cycle, the compressor of a vapor-compression type refrigerating machine is also used as an expander, that is, the compressor is used both as a compressor and an expander. Therefore, in the case where energy is recovered by the Rankine cycle, the compressor is used as an expander.
However, the following problems may be encountered in the conventional machine. In the case where a scroll type pump is employed as a compressor/expander as described above and compression/expansion is conducted by a normal/reverse rotating motion, the machine is usually designed mainly as a compressor which is operated when a vapor-compression type refrigerating machine is operated. Therefore, when the machine is operated as an expander, the performance of the compressor may not be satisfactory.
Specifically, one of the problems is the opening and closing motion of the suction port of the machine in the case where the machine is used as an expander. In the case where the scroll pump is used as a compressor, it is common that a counterflow of the refrigerant from the high pressure side to the low pressure side is prevented by a discharge valve which is opened and closed by a difference in pressure. This method of preventing the counterflow of the refrigerant is easily executed. However, in the case where the scroll pump is used as an expander, the applying of a valve for preventing the leakage of refrigerant from the high pressure side to the low pressure side is not easy, because the structure becomes complicated and the size is increased. Therefore, in order to prevent leakage of refrigerant from the high pressure side into the operating chamber at the time of the expansion mode, it is preferable that useless leakage of refrigerant be suppressed by enhancing the sealing property of the scroll portion.
Importance is attached to the sealing property by which the leakage of refrigerant from the high pressure side to the low pressure side is suppressed as described above. On the other hand, in order to obtain a continuous and stable flow of refrigerant, it is important that the operating chambers, which are successively formed at the scroll center at the time of the expansion mode, are instantaneously changed over. When the discharge port at the time of the compression mode is used as a suction port at the time of the expansion mode, the suction port is closed over too long a period of time at the time when the operating chamber is changed over, and the operating chamber can not be changed over smoothly.
The present inventors paid attention to the above specific problems and found that the performance at the time when the machine was operated as an expander could be enhanced by appropriately setting the suction port and the scroll center at the time of the expansion mode.